An environmentally-friendly vehicle having an engine and at least one drive motor is being developed corresponding to a demand for improving fuel consumption efficiency and an exhaust gas regulation reinforcement.
An environmentally-friendly vehicle includes a fuel cell vehicle, an electric vehicle, a plug-in electric vehicle, and so on, and uses high voltage/high current power to generate a driving torque.
An environmentally-friendly vehicle includes a motor generating a demanded driving torque, an inverter controlling the motor, and a DC/DC converter that boosts a voltage of 350 to 450 V stored in a battery to supply the boosted voltage to the inverter.
The DC-DC converter is a bidirectional booster type, is disposed between the high voltage battery and the inverter, and boosts a low voltage to a high voltage.
While the PWM converter is boosting the voltage, the environmentally-friendly vehicle detects the current that is outputted by the inductor to perform current control and power limitation. And, an inverter detects current flowing each phase of a motor to control current and generates driving force of a motor through the current control
The current of the inductor has a pulsatory (chopping wave) shape that repeatedly ascends and descends with a predetermined slope according to the switching condition of a power switching element.
In this condition, one cycle average current value that is outputted from the inductor is used to limit the boosted current and the outputted power.
FIG. 8 shows an offset of an inductor current in a DC-DC converter for a conventional environmentally-friendly vehicle.
Referring to FIG. 8, when first and second switching elements are switched according to a first PWM duty signal (PWM P) and a second PWM duty signal (PWM N) that is transmitted from a controller, a delay of Td1 and Td2 against output is formed in a real output current (Ideal) and a detected current (Real) of an inductor by on/off delay of the first and second switching elements, a phase delay of a current sensor, a phase delay of a filter circuit, and so on to generate a±offset value.
Accordingly, the offset generation of an inductor current in the PWM converter affects the control precision (current control and torque control) and the current related protection function.
Because the sensing delay of the inductor current is inevitable, a power module in which the on/off characteristic is fast and a sensor and a filter circuit in which phase delay responsiveness is excellent are used so as to minimize the delay, but these elements are very expensive and elements satisfying the terms desired by the environmentally-friendly vehicle are very limited.
In a condition in which a difference between real timing in which the current is outputted from an inductor and measured timing thereof is formed, a power limitation function can malfunction by an error of a current measurement timing during maximum driving and regenerative braking of a real vehicle to be able to generate a problem of stopping the vehicle from driving.
In a conventional environmentally-friendly vehicle, an A/D sensing delay method, a phase delay method, an average current calculation method, and so on are applied to measure the inductor current of the DC-DC converter.
The A/D sensing delay method estimates a delay time (tdelay) for an error between real timing in which the current is output from an inductor and measurement timing thereof through hardware (H/W) using a sensor or an estimation method through software (S/W) to adjust the measurement timing of the inductor current.
However, the method has a problem that it has a limitation for calculation of a processor for controlling current in digital control.
The phase delay method delays the phase of the current measured by 90 degrees, and this method can be applied to a system in which the control responsiveness is relatively slow, but cannot be applied to a system in which the control responsiveness is fast.
Also, the average current calculation method calculates an average current through current sampling twice for one cycle to demand multiple sampling for one cycle, and therefore the method can be applied to a control method that demands control once within one cycle but is incongruent with a control method that demands multiple control within one cycle.
Also, in a condition in which a delay of the measured time is larger than a transmitted PWM duty signal, there is a problem that an error is generated when compensating the offset value.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it can contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.